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            <small>
              <a href="#Procedure">Procedure<br></a>
              <a href="#Abstract">Abstract<br></a>
              <a href="#Required_Reading">Required_Reading<br></a>
              <a href="#Keywords">Keywords<br></a>
              <a href="#Brief_I/O">Brief_I/O<br></a>
              <a href="#Detailed_Input">Detailed_Input<br></a>

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              <small>               <a href="#Detailed_Output">Detailed_Output<br></a>
              <a href="#Parameters">Parameters<br></a>
              <a href="#Exceptions">Exceptions<br></a>
              <a href="#Files">Files<br></a>
              <a href="#Particulars">Particulars<br></a>
              <a href="#Examples">Examples<br></a>

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              <small>               <a href="#Restrictions">Restrictions<br></a>
              <a href="#Literature_References">Literature_References<br></a>
              <a href="#Author_and_Institution">Author_and_Institution<br></a>
              <a href="#Version">Version<br></a>
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<h4><a name="Procedure">Procedure</a></h4>
<PRE>
   SpiceDouble vrel_c ( ConstSpiceDouble v1[3],
                        ConstSpiceDouble v2[3]  )

</PRE>
<h4><a name="Abstract">Abstract</a></h4>
<PRE>
   Return the relative difference between two 3-dimensional vectors.
</PRE>
<h4><a name="Required_Reading">Required_Reading</a></h4>
<PRE>
   None.
</PRE>
<h4><a name="Keywords">Keywords</a></h4>
<PRE>
   MATH
   VECTOR


</PRE>
<h4><a name="Brief_I/O">Brief_I/O</a></h4>
<PRE>
   Variable  I/O  Description
   --------  ---  --------------------------------------------------
    v1,v2     I   Input vectors.
</PRE>
<h4><a name="Detailed_Input">Detailed_Input</a></h4>
<PRE>
    v1, v2        are two 3-dimensional vectors for which the
                  relative difference is to be computed.
</PRE>
<h4><a name="Detailed_Output">Detailed_Output</a></h4>
<PRE>
    <b>vrel_c</b>        the relative difference between V1 and V2.
                  It is defined as:
                                              || v1 - v2 ||
                            <b>vrel_c</b>   =   ----------------------
                                       max ( ||v1||, ||v2|| )

                  where || x || indicates the Euclidean norm of
                  the vector x ( ||x|| = sqrt( x . x ) ).

                  <b>vrel_c</b> assumes values in the range [0,2]. If both
                  v1 and v2 are zero vectors then <b>vrel_c</b> is defined
                  to be zero.
</PRE>
<h4><a name="Parameters">Parameters</a></h4>
<PRE>
   None.
</PRE>
<h4><a name="Exceptions">Exceptions</a></h4>
<PRE>
   Error free.

   If both v1 and v2 are zero vectors then <b>vrel_c</b> is defined
   to be zero.
</PRE>
<h4><a name="Files">Files</a></h4>
<PRE>
   None.
</PRE>
<h4><a name="Particulars">Particulars</a></h4>
<PRE>
   This function computes the relative difference between two
   3-dimensional vectors as defined above.

   The function <a href="vrelg_c.html">vrelg_c</a> may be used to find the relative difference
   for two vectors of general dimension.
</PRE>
<h4><a name="Examples">Examples</a></h4>
<PRE>
   This example code fragment computes the relative difference
   between the geometric and light time corrected state of Io
   with respect to Voyager 2 at a given UTC time.

         #include &quot;SpiceUsr.h&quot;
               .
               .
               .
         /.
         The NAIF integer code for Io is 501 and the code for
         Voyager 2 is -32.
         ./

         #define           IO    501
         #define           VG2   -32


         /.
         Local variables
         ./
         SpiceDouble       state [ 6 ];
         SpiceDouble       pos1  [ 3 ];
         SpiceDouble       pos2  [ 3 ];
         SpiceDouble       diff;
         SpiceDouble       lt;
         SpiceDouble       et;

         SpiceChar       * utc = &quot;1979 JUN 25 12:00:00&quot;;

         /.
         Load the sample SPK ephemeris file.
        ./
         <a href="furnsh_c.html">furnsh_c</a> ( &quot;VG2_JUP.BSP&quot; );


         /.
         Convert the UTC time string to ephemeris time.
         ./
         <a href="utc2et_c.html">utc2et_c</a> ( utc, &amp;et );


         /.
         First calculate the geometric state and then the light
         time corrected state.
         ./
         <a href="spkez_c.html">spkez_c</a> ( IO, et, &quot;J2000&quot;, &quot;none&quot;, VG2, state, &amp;lt );

         <a href="vequ_c.html">vequ_c</a>  ( state, pos1 );

         <a href="spkez_c.html">spkez_c</a> ( IO, et, &quot;J2000&quot;, &quot;lt&quot;, VG2, state, &amp;lt );

         <a href="vequ_c.html">vequ_c</a>  ( state, pos2 );

         /.
         Call <b>vrel_c</b> to find the relative difference between the
         two states.
         ./
         diff = <b>vrel_c</b> ( pos1, pos2 );

         .
         .
         .
</PRE>
<h4><a name="Restrictions">Restrictions</a></h4>
<PRE>
   None.
</PRE>
<h4><a name="Literature_References">Literature_References</a></h4>
<PRE>
   None.
</PRE>
<h4><a name="Author_and_Institution">Author_and_Institution</a></h4>
<PRE>
   J.M. Lynch     (JPL)
   E.D. Wright    (JPL)
</PRE>
<h4><a name="Version">Version</a></h4>
<PRE>
   -CSPICE Version 1.1.0, 28-AUG-2001 (NJB)
     
      Include interface macro definition file SpiceZim.h. 

   -CSPICE Version 1.0.1, 13-APR-2000 (NJB) 
   
      Made some minor updates and corrections in the code example.
      
   -CSPICE Version 1.0.0, 6-JUL-1999
</PRE>
<h4><a name="Index_Entries">Index_Entries</a></h4>
<PRE>
   relative difference of 3-dimensional vectors
</PRE>
<h4>Link to routine vrel_c source file <a href='../../../src/cspice/vrel_c.c'>vrel_c.c</a> </h4>

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   <pre>Wed Jun  9 13:05:32 2010</pre>

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